Radio Frequency (RF) filters have been used with cellular base stations and other telecommunications equipment for some time. Such filters are conventionally used to filter out noise and other unwanted signals. For example, bandpass filters are conventionally used to filter out or block radio frequency signals in all but one or more predefined band(s). By way of another example, notch filters are conventionally used to block signals in a predefined radio frequency band.
The relatively recent advancements in superconducting technology have given rise to a new type of RF filter, namely, the high temperature superconducting (HTSC) filter. HISC filters contain components which are superconductors at or above the liquid nitrogen temperature of 77 K. Such filters provide greatly enhanced performance in terms of both sensitivity (the ability to select signals) and selectability (the ability to distinguish desired signals from undesirable noise and other traffic) as compared to conventional filters. However, since known high temperature superconducting (HTSC) materials are only superconductive at relatively low temperatures (e.g., approximately 90 K or lower), and are relatively poor conductors at ambient temperatures, such superconducting filters require accompanying cooling systems to ensure the filters are maintained at the proper temperature during use. As a result, the reliability of traditional superconducting filters has been tied to the reliability of the power source. Specifically, if the power source (e.g., a commercial power distribution system) fails (e.g., a black out, a brown out, etc.) for any substantial length of time, the cooling system would likewise fail and, when the corresponding superconducting filters warm sufficiently to prevent superconducting, so too would the filters.
To prevent systems serviced by such filters from failing during these power outages, additional circuitry in the form of RF bypass circuitry was often needed to switch out the failed filter until a suitably cooled environment was returned. Such bypass circuitry added expense and complexity to known systems.